Electromagnetic base for magnetic drill press

ABSTRACT

A drill press includes a main housing, a drill unit supported by the main housing for relative movement therewith, and a magnetic base for coupling the drill press to a ferromagnetic workpiece. The magnetic base includes a ferromagnetic body having spaced, substantially parallel first and second rails. Each of the first and second rails includes a flat bottom surface engageable with the ferromagnetic workpiece. A coil is positioned between the first and second rails for generating a holding force on the ferromagnetic workpiece. The coil defines a central axis that is parallel with the bottom surface of each of the first and second rails.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/639,559 filed Mar. 5, 2015, which claims priority to U.S.Provisional Patent Application No. 61/949,296 filed on Mar. 7, 2014, theentire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to electromagnetic bases, and morespecifically to electromagnetic bases for use with drill presses.

BACKGROUND OF THE INVENTION

Magnetic drill presses perform drilling operations by magneticallylatching a base of the drill press to a ferromagnetic workpiece. Themagnetic base of the drill press may be switchable between magnetizedand demagnetized states using electromagnets or permanent magnets.

SUMMARY OF THE INVENTION

The invention provides, in one aspect, a drill press including a mainhousing, a drill unit supported by the main housing for relativemovement therewith, and a magnetic base for coupling the drill press toa ferromagnetic workpiece. The magnetic base includes a ferromagneticbody having spaced, substantially parallel first and second rails. Eachof the first and second rails includes a flat bottom surface engageablewith the ferromagnetic workpiece. A coil is positioned between the firstand second rails for generating a holding force on the ferromagneticworkpiece. The coil defines a central axis that is parallel with thebottom surface of each of the first and second rails.

The invention provides, in another aspect, a drill press including amain housing, a drill unit supported by the main housing for relativemovement therewith, and a magnetic base for coupling the drill press toa ferromagnetic workpiece. The magnetic base includes a ferromagneticbody having spaced, substantially parallel first and second rails. Eachof the first and second rails includes a flat bottom surface engageablewith the ferromagnetic workpiece. A coil is positioned between the firstand second rails for generating a holding force on the ferromagneticworkpiece. Each of the first and second rails includes a chamferadjacent the flat bottom surface and on an interior edge of therespective first and second rails.

Other features and aspects of the invention will become apparent byconsideration of the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a drill press including anelectromagnetic base in accordance with an embodiment of the invention.

FIG. 2 is a bottom perspective view of a prior art electromagnetic baseincluding two cylindrical coils.

FIG. 3 is a perspective view of the electromagnetic base of FIG. 1.

FIG. 4 is an end view of the electromagnetic base of FIG. 3 with the endcaps, the bobbin, and the coil removed.

FIG. 5 is an end view of the electromagnetic base of FIG. 3 with the endcaps and the coil removed.

FIG. 6 is an end view of the electromagnetic base of FIG. 3 with the endcaps removed.

FIG. 7 is a cross-sectional view of the electromagnetic base of FIG. 3positioned on a flat workpiece, schematically showing a magnetic fluxpath through the workpiece.

FIG. 8 is a cross-sectional view of the prior art electromagnetic baseof FIG. 2 positioned on a flat workpiece, schematically showing multiplemagnetic flux paths through the workpiece.

FIG. 9 is a cross-sectional view of the electromagnetic base of FIG. 3positioned on a cylindrical workpiece, schematically showing a magneticflux path through the workpiece.

FIG. 10 is a perspective view of an electromagnetic base in accordancewith another embodiment of the invention.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

DETAILED DESCRIPTION

FIG. 1 illustrates a magnetic drill press 10 including a drill unit 14,a main housing 18 to support the drill unit 14, and a magnetic base 22coupled to the main housing 18 and selectively magnetically latching themagnetic drill press 10 to a ferromagnetic workpiece (FIGS. 7 and 9).The drill unit 14 may include a DC motor or an AC motor to rotate aspindle 26 with a working tool attached thereto about a rotational axis28. The drill unit 14 is supported by the main housing 18 for relativemovement therewith in a direction along the rotational axis 28. Themagnetic drill press 10 may be powered by a battery, from an AC voltageinput 30 (i.e., from a wall outlet) as shown in the illustratedembodiment, or by an alternative DC voltage input (e.g., a DC powersupply).

With reference to FIG. 2, a prior art magnetic base 34 for use with adrill press includes a ferromagnetic body 38 and two cylindricalelectromagnet coils 42 having respective central axes that are normal toa flat bottom surface 46 of the ferromagnetic body 38. The electromagnetcoils 42 are energized by a power source (not shown) to magnetize theferromagnetic body 38 and attach the bottom surface 46 to a flatworkpiece or other ferromagnetic substrate (FIG. 8). The prior art base34, however, only provides a single line of contact between the flatbottom surface 46 and a cylindrical or convex surface, which preventsthe base 34 from sitting stably on a pipe, for example. Furthermore, thebase 34 requires ferromagnetic material located above the electromagnetcoils 42 to complete the magnetic circuit and generate the flux pathsshown in FIG. 8, which adds to the overall weight of the base 34.Finally, the base 34 is not easily scaled in size and fixed dimensionalproportions are required to maintain the magnetic properties of the base34. A more detailed discussion of the deficiencies of the prior art base34 and comparisons to the magnetic base 22 of the invention is providedthroughout this description.

With reference to the present invention and to FIGS. 3-6, the magneticbase 22 includes a ferromagnetic body 50 having spaced, substantiallyparallel first and second rails 54, 58 (FIGS. 4-6). Each of the firstand second rails 54, 58 includes a top surface 62 and a flat, bottomsurface 66 that is engageable with a flat ferromagnetic workpiece 70(FIG. 7). Each of the first rail 54 and the second rail 58 also includesa chamfer 74 on an interior edge 78 adjacent the bottom surface 66 ofthe respective rails 54, 58 (FIGS. 4-6). The magnetic base 22 alsoincludes a coil 82 supported on a bobbin 86 and positioned between thefirst and second rails 54, 58 for generating a holding force on theferromagnetic workpiece 70 when the coil 82 is energized. The coil 82 isspaced from the flat bottom surface 66 of each of the first and secondrails 54, 58, and the coil 82 defines a central axis 90 (FIG. 6)parallel with the bottom surface 66 of each of the first and secondrails 54, 58. In other words, when the magnetic base 22 is attached to aflat workpiece 70 to thereby support the drill unit 14 such that therotational axis 28 is generally perpendicular to the ground, the coil 82is oriented with the central axis 90 substantially horizontal (FIG. 7).The coil 82 is configured as a bipolar electromagnet and is the onlycoil 82 incorporated in the base 22 for generating a workpiece-holdingforce.

With reference to FIG. 4, the ferromagnetic body 50 includes a rib 94interconnecting the first rail 54 and the second rail 58. The rib 94interconnects the first rail 54 and the second rail 58 at a positionspaced from the flat bottom surface 66 and the top surface 62 of each ofthe first and second rails 54, 58. In other words, the rib 94 ispositioned intermediate the top surface 62 and the bottom surface 66 ofthe first and second rails 54, 58. Alternatively, the rib 94 may besubstantially aligned with the top surface 62 of the respective rails54, 58 (FIG. 10).

The base 22 further includes a non-ferromagnetic plate 96 extendingbetween the first rail 54 and the second rail 58 (FIG. 4). Thenon-ferromagnetic plate 96 is positioned beneath and spaced from thecoil 82. The non-ferromagnetic plate 96 is also positioned above andspaced from the chamfers 74. A groove 100 is formed in an interiorsurface 104 of each of the first rail 54 and the second rail 58 suchthat the non-ferromagnetic plate 96 is slidably received within therespective grooves 100. As explained in further detail below, thenon-ferromagnetic plate 96 protects the bottom of the coil 82 fromcontact with the workpiece or anything else.

With reference to FIG. 9, the chamfer 74 on the each of the first andsecond rails 54, 58 enables the base 22 to be supported on a convex orcylindrical surface 108 (e.g., a pipe). In some embodiments, thechamfers 74 are inclined relative to the respective bottom surfaces 66between about 10 degrees and about 12 degrees. Alternatively, thechamfers 74 may be inclined relative to the respective bottom surfaces66 between about 8 degrees and about 14 degrees. In the illustratedembodiment, the chamfers 74 are inclined relative to the respectivebottom surfaces 66 by about 11 degrees and are suitable to support thebase 22 on a 6-inch diameter (i.e., schedule 40) pipe. As explained infurther detail below, the chamfers 74 modify the magnetic properties ofthe ferromagnetic body 50, and allow the base 22 to achieve acceptableholding strength on both thick and thin workpieces.

With reference to FIG. 5, the bobbin 86 is shown positioned around therib 94 with the coil 82 removed. The bobbin 86 includes a first portion112 and a second portion 116 that are interconnected by an overlappingjoint 120. In particular, the overlapping joint 120 is a labyrinth jointthat is assembled by snap-fitting the first portion 112 and the secondportion 116 together. The overlapping joint 120 prevents any splitswithin the insulating material between the coil 82 and the ferromagneticbody 50, and increases the dielectric strength of the insulation. Withreference to FIG. 7, a first insulation layer 124 (i.e., a flange of thefirst portion 112) is positioned between the first rail 54 and the coil82, and a second insulation layer 128 (i.e., an opposite flange of thefirst portion 112) is positioned between the second rail 58 and the coil82. In the illustrated embodiment, as a result of orienting the coil 82with its central axis 90 parallel to the bottom surfaces 66 of therespective rails 54, 58, there are no more than two layers of insulation124, 128 located within a width dimension 132 defined between the firstrail 54 and the second rail 58. In contrast, the prior art base 34includes four layers of insulation 168 within a width dimension 172 ofthe prior art base 34. By reducing the number of insulation layerswithin the width dimension 132, the overall width of the magnetic base22 is reduced compared to the width of the prior art base 34. Also, byreducing the number of insulation layers within the width dimension 132,a higher coil density (i.e., more power) can be achieved compared to theprior art base 34. In alternative embodiments, dielectric tape or a coilovermold could replace the bobbin 86. As a further alternative, theferromagnetic body can be cut down the center so the bobbin can remainwhole and the coil wound separately before the ferromagnetic body halvesare joined back together with the bobbin and wound coil.

With reference to FIG. 3, the magnetic base 22 further includes a firstend cap 136 coupled to a front end 140 of the ferromagnetic body 50 anda second end cap 144 coupled to a rear end 148 of the ferromagnetic body50. The first and second end caps 136, 144 are made from anon-ferromagnetic material (e.g., stainless steel or aluminum). Thefirst and second end caps 136, 144 are secured to the ferromagnetic body50 via fasteners 152, or the like. The first end cap 136, the second endcap 144, and the non-ferromagnetic plate 96 at least partially enclosethe coil 82, thereby protecting it from inadvertent contact with theworkpiece or anything else. The second end cap 144 includes a mountingportion 156 that extends above the ferromagnetic body 50 and engages themain housing 18 to secure the base 22 and the main housing 18 together.In this instance, the main housing 18 is coupled to the top surface 62of each of the first and second rails 54, 58, thereby functioning as atop cap enclosing an upper portion of the coil 82. The first and secondrails 54, 58 also extend above and below the coil 82. Accordingly, themain housing 18, the first end cap 136, the second end cap 144, and thenon-ferromagnetic plate 96 completely enclose the coil 82.

With reference to FIG. 7, the base 22 is magnetically latched to a topsurface of the flat workpiece 70, schematically illustrating a singlemagnetic flux path 160 passing through a wide portion of the workpiece70. In contrast, FIG. 8 illustrates the prior art base 34 magneticallylatched to a top surface of the flat workpiece 70, schematicallyillustrating multiple (e.g., two) magnetic flux paths 164 passingthrough more narrow portions of the workpiece 70. Regarding the priorart base 34 of FIG. 8, the flux paths 164 pass through ferromagneticmaterial with various cross-sections, and ferromagnetic material isrequired above the coil 42 to complete the magnetic circuit. Inaddition, the flat bottom surface 46 across the entire width of theprior art base 34 is required to complete the magnetic circuit throughthe flat workpiece 70. In contrast, with the base 22 of FIG. 7, the fluxpath 160 travels through ferromagnetic material with a substantiallyuniform cross-section from one side of the base 22 to the other becausethe rails 54, 58 and the rib 94 have similar cross-sectional areas.

The magnetic base 22 is an improvement over the prior art base 34because the dimensions of the magnetic base 22 can be reduced moreeasily to reduce the overall width of the drill press 10 in which thebase 22 is used. Reducing the width of the drill press 10 is desirablein many applications. For example, the magnetic base 22 allows a user todrill in hard to reach places such as the inside of an I-beam, in whichwidth is limited but the height and length of the drill press are not asrestrictive. The magnetic base 22 can be modified to increase theoverall length of the base, and such a modification would not affect thelength of the magnetic flux path 160. In other words, because theferromagnetic body 50 is symmetrical, it is more suitable for scaling.In contrast, if the length of the prior art base 34 is increased, thelength of the magnetic flux path 164 increases, which increasesreluctance and decreases the strength of the magnetic field. Increasingthe length of the prior art base 34 also requires a more proportionalchange in the width of the base 34 because it is important to maintain auniform cross-section for the magnetic flux path to travel through. As aresult, the base 22 can be made longer and narrower than the prior artbase 34. Increasing the base length also provides an increasedresistance to a reactionary moment (caused by a reaction to the workingtool engaging the workpiece) acting to lift the base 22 off theworkpiece 70. In this scenario, the drill press 10 will tend to pivot onthe rear of the base 22 as the working tool plunges into the workpiece70. A longer electromagnetic base 22 will better resist this momentcompared to the prior art electromagnetic base 34.

The base 22, which includes just a single coil 82, maximizes themagnetic field strength within the ferromagnetic body 50. Anotherbenefit to including only the single coil 82 within the base 22 is thata ferromagnetic body can only dissipate so much heat, which limits theamount of power that can be applied to the coil(s). With a limitedpower, the total amp-turns of the coil(s) in the electromagnetic base ofa given size are similar whether there is one coil or multiple coils.With multiple coils, however, the total amp-turns may be less becausecoil space must be sacrificed for additional insulation. As describedabove and with reference to FIGS. 7 and 8, there are only two layers ofinsulation 124, 128 across the width dimension 132 of base 22 (FIG. 7),whereas the prior art base 34 includes at least four layers ofinsulation 168 across a width dimension 172 (FIG. 8). Accordingly, thecoil density in the base 22 is greater than that in the prior art base34.

The magnetic drill press 10 is utilized on workpieces having differentthickness, and the magnetic base 22 is operable to create adequateholding force for both thick (e.g., ¾″ and thicker) and thin (e.g., ⅜″and thinner) workpieces. With only the single coil 82, there is only oneflux path 160 through the workpiece. Thin materials can saturate easily,causing the holding force to deteriorate. As explained below, thechamfers 74 allow for tuning of the holding force generated by the coil82 on different material thicknesses. The holding force is proportionalto the cross-sectional area of the magnetic flux path and proportionalto the flux density squared. For a thinner workpiece, the magnetic fluxis choked off by the high reluctance of a narrow magnetic flux paththrough the thin workpiece. When the cross-sectional area of the fluxpath is reduced at the bottom surface 66 (i.e., by including a largechamfer), the reluctance of the flux path through the body 50 is changedvery little. However, this reduction in the surface area of the bottomsurfaces 66 will increase the flux density at the bottom surfaces 66.The increase in flux density has a greater positive effect on holdingforce than the negative effect from the decrease in cross-sectional areaof the path, because holding force is proportional to the square of fluxdensity. Therefore, a large chamfer increases the holding force on athinner workpiece. As such, the chamfers 74 are designed to tune theferromagnetic body 50 in order to achieve an acceptable holding forcefor both thick and thin workpieces.

The prior art magnetic base 34 (which includes multiple coils) issufficient for magnetically latching to flat or smooth workpieces, butthe holding force capable of being developed by the prior art base 34 issubstantially reduced when an air gap is introduced between the base 34and the workpiece. Such air gaps might result from rust, paint, orimperfections on the surface of the workpiece, thereby deteriorating theholding force which the prior art magnetic base 34 is otherwise capableof creating. This is a result of the holding force being proportional tothe square of flux density, which is in turn proportional to amp-turns(of a magnetic coil) divided by the reluctance of the magnetic circuit(assuming a constant cross-sectional area through the flux path). Whenan air gap is introduced, the reluctance of the magnetic circuitincreases and causes the magnetic flux to decrease. Assuming the sametotal amp-turns, the magnetic flux (and in turn the holding force)decreases more substantially when an air gap is introduced in the priorart base 34 with multiple coils than in the base 22 with the single coil82, because one of multiple coils in the prior art base 34 representsonly a fraction of the total amp-turns. In other words, with a fractionof the total amp-turns in the region of the air gap, the magnetic fluxand holding force through this region are more substantially decreasedcompared to the base 22 with a single coil having the total amp-turns inthe region of the air gap. As such, the reluctance added by an air gapmore significantly affects an electromagnetic base with multiple coils(such as the prior art base 34) than an electromagnetic base with only asingle coil (such as the magnetic base 22).

With reference to FIG. 9, the base 22 is configured to support the drillpress 10 on a convex or cylindrical surface 108 (e.g., a pipe). Ratherthan the first and second rails 54, 58 being in contact with the surface108, the chamfers 74 engage the workpiece 108, thereby providing atleast two regions of contact between the base 22 and the workpiece 108.A workpiece receiving space 176 is defined between the first rail 54,the second rail 58, and the non-ferromagnetic plate 96 in which aportion of the workpiece 108 is received. Unlike the prior art base 34shown in FIG. 8, the base 22 does not require an adaptor or additionalattachments in order to be supported on the cylindrical workpiece 108(FIG. 9).

With reference to FIG. 10, a magnetic base 180 in accordance withanother embodiment of the invention is illustrated including aseparately removable top cap 184 positioned above the coil 82 andcoupled to a top surface 62 of each of a first and second rails 54, 58.The top cap 184 is made from a non-ferromagnetic material (e.g.,aluminum) having a density less than that of the ferromagnetic body 50.Although end caps like those shown in FIG. 3 are not illustrated forclarity, it should be understood that the top cap 184 in associationwith end caps and a non-ferromagnetic plate (like plate 96) maypartially or completely enclose the coil 82.

Various features and advantages of the invention are set forth in thefollowing claims.

What is claimed is:
 1. A drill press comprising: a main housing; a drillunit supported by the main housing for relative movement therewith; anda magnetic base coupled to the main housing for coupling the drill pressto a ferromagnetic workpiece, the magnetic base including aferromagnetic body including spaced, substantially parallel first andsecond rails, each of the first and second rails having a flat bottomsurface engageable with the ferromagnetic workpiece, and a coilpositioned between the first and second rails for generating a holdingforce on the ferromagnetic workpiece, wherein the coil defines a centralaxis parallel with the bottom surface of each of the first and secondrails.
 2. The drill press of claim 1, wherein the ferromagnetic bodyincludes a rib interconnecting the first rail and the second rail, andwherein the coil surrounds the rib.
 3. The drill press of claim 2,wherein the rib is located between the bottom surface and a top surfaceof each of the first rail and the second rail.
 4. The drill press ofclaim 3, wherein each of the first rail and the second rail areferromagnetic from the top surface to the bottom surface.
 5. The drillpress of claim 1, wherein each of the first rail and the second railincludes a chamfer on an interior edge adjacent the bottom surface ofeach of the first and second rails.
 6. The drill press of claim 1,further comprising a non-ferromagnetic plate extending between the firstrail and the second rail, wherein the non-ferromagnetic plate ispositioned beneath and spaced from the coil.
 7. The drill press of claim6, further comprising: a first end cap coupled to a front end of theferromagnetic body; and a second end cap coupled to a rear end of theferromagnetic body, wherein the first and second end caps are made froma non-ferromagnetic material, and wherein the first end cap, the secondend cap, and the non-ferromagnetic plate at least partially enclose thecoil.
 8. The drill press of claim 6, further comprising a groove formedin an interior surface of each of the first rail and the second rail,wherein the non-ferromagnetic plate is received within the groove ofeach of the first rail and the second rail.
 9. The drill press of claim6, wherein a workpiece receiving space is defined between the firstrail, the second rail, and the non-ferromagnetic plate.
 10. The drillpress of claim 1, further comprising a bobbin upon which the coil issupported, wherein the bobbin includes a first portion and a secondportion that are interconnected by an overlapping joint.
 11. The drillpress of claim 1, further comprising a first insulation layer positionedbetween the first rail and the coil, and a second insulation layerpositioned between the second rail and the coil, wherein a widthdimension is defined between the first rail and the second rail, andwherein no more than two layers of insulation are located within thewidth dimension.
 12. The drill press of claim 1, further comprising atop cap positioned above the coil and coupled to a top surface of eachof the first and second rails, wherein the top cap is made from anon-ferromagnetic material, and wherein the top cap encloses an upperportion of the coil.
 13. The drill press of claim 1, wherein the coil isa bipolar electromagnet.
 14. The drill press of claim 1, wherein thecoil is spaced from the flat bottom surface of each of the first andsecond rails.
 15. The drill press of claim 1, wherein the coil is theonly coil coupled to the ferromagnetic body.
 16. The drill press ofclaim 1, wherein the ferromagnetic body is H-shaped.
 17. A drill presscomprising: a main housing; a drill unit supported by the main housingfor relative movement therewith; and a magnetic base for coupling thedrill press to a ferromagnetic workpiece, the magnetic base including aferromagnetic body including spaced, substantially parallel first andsecond rails, each of the first and second rails having a flat bottomsurface engageable with the ferromagnetic workpiece, and a coilpositioned between the first and second rails for generating a holdingforce on the ferromagnetic workpiece, wherein each of the first andsecond rails includes a chamfer adjacent the flat bottom surface and onan interior edge of the respective first and second rails.
 18. The drillpress of claim 17, wherein the chamfer is inclined between 10 degreesand 12 degrees relative to the flat bottom surface.
 19. The drill pressof claim 17, further comprising a non-ferromagnetic plate extendingbetween the first rail and the second rail, wherein thenon-ferromagnetic plate is positioned between the coil and the chamferof each of the first and second rails.
 20. The drill press of claim 19,wherein a workpiece receiving space is defined between the first rail,the second rail, and the non-ferromagnetic plate.
 21. The drill press ofclaim 20, wherein the first rail and the second rail are configured tosupport the magnetic base on a round workpiece, and wherein a portion ofthe round workpiece is received within the workpiece receiving space.22. The drill press of claim 17, wherein the chamfers of the respectivefirst and second rails are engageable with a round workpiece.
 23. Thedrill press of claim 17, wherein the ferromagnetic body includes a ribinterconnecting the first rail and the second rail, and wherein the coilsurrounds the rib, and wherein the rib is located between the flatbottom surface and a top surface of each of the first rail and secondrail, and wherein each of the first rail and the second rail areferromagnetic from the top surface to the bottom surface.
 24. The drillpress of claim 17, wherein the ferromagnetic body is H-shaped.